Mammalian mitochondria contain 55S ribosomes of unusual composition and physical-chemical properties. The proposed research will use immunochemical methods to analyze the protein composition of mammalian mitochondrial ribosomes, and to elucidate the biosynthesis and functional roles of several of the proteins of mammalian mitochondria. Mitochondrial ribosomes prepared on a large scale from bovine liver will be used to produce antibodies in rabbits and the mouse hybridoma system against (a) ribosomes, (b) subribosomal particles, and (c) total protein extracts of subribosomal particles. These antisera and enriched immunoglobulins (IgG) will be used in a variety of studies: 1. Structural studies. Antibodies directed against subunits of mitochondrial ribosomes will be used to discriminate between comigrating proteins (2-dimensional electrophoresis) from both subunits, and to establish an upper limit for the number of different proteins contained in bovine mitochondrial ribosomes. 2. Immunochemical homology. Experiments will be done to ascertain which proteins of mitochondrial ribosomes are immunochemically homologous to proteins in other ribosomes. 3. Functional studies. IgG and fab fragments prepared from IgG reacting with individual r-proteins will be used to implicate these proteins in defined ribosome functions by their inhibitory action in cell-free assays of ribosome function. 4. Biosynthetic studies. Antibodies against mitochondrial r-proteins will be used to identify the class of cytoplasmic ribosomes involved in synthesizing most of these proteins, and to determine the nature of their cellular pools.